An internal combustion engine converts the chemical energy of the combustion fuel into mechanical energy to produce driving force. The internal combustion engine typically includes one or a plurality of reciprocating pistons that operate to drive a crankshaft. The crankshaft converts the reciprocal motion of the pistons to rotational motion. The pistons are slidably disposed within cylinders defined by a cylinder block or case. A cylinder head is removably mounted to the cylinder case and cooperates with the pistons and their respective bores to form variable volume combustion chambers within which the combustion of fuel occurs.
The cylinder head typically contains spark plugs, inlet valves, exhaust valves, and may contain one or a plurality of camshafts. Much of the valvetrain may be mounted with respect to the cylinder head. Generally, the cylinder head is an aluminum or iron casting that defines a portion of the variable volume combustion chambers, intake ports, and exhaust ports. The intake ports operate to communicate air or an air-fuel mixture to the variable volume combustion chamber, while the exhaust ports operate to exhaust products of combustion from the variable volume combustion chamber. An exhaust manifold is typically removably mounted to the cylinder head using conventional fastening techniques, such as threaded fasteners. Additionally, a gasket may be provided between the cylinder head and the exhaust manifold for sealing purposes. The exhaust manifold is typically formed from stainless steel or cast iron and includes runner portions in communication with each of the exhaust ports of the cylinder head. Additionally, the exhaust manifold typically includes a collector volume, in fluid communication with each of the exhaust runner portions, which operates to communicate the products of combustion to the downstream components of the vehicle exhaust system, such as catalytic converters and mufflers. The cylinder head and cylinder case define a series of passages or cooling jackets that facilitate coolant flow. Coolant is circulated through the cooling jackets to cool the cylinders and the general area above the combustion chambers.
Recently, engine manufacturers have designed cylinder heads wherein the exhaust manifold, i.e. the exhaust runners and collector volume are internally defined by the cylinder head casting to form an integral exhaust manifold. These designs typically include exhaust ports and exhaust runners that are configured in a generally orthogonal relation to the collector volume forming a “log style” exhaust manifold.